1. (Field of the Invention)
The present invention generally relates to the measurement of the dynamic roundness of a commutator employed in a commutator motor and, more particularly, to an apparatus for and a method of testing the commutator to evaluate the quality of the commutator as assembled.
2. (Description of the Prior Art)
One of the factors that are determinative of the lifetime of the commutator motor of a kind used in, for example, a vacuum cleaner is reliability of a commutator. If during a high speed rotation of the commutator motor the commutator encounters a trouble such as, for example, radial lift of one or some of the commutator segments and/or eccentricity of the commutator, one or both of brushes held in sliding contact with the commutator will instantaneously separate from their contact with the commutator segments a slight distance corresponding to deformation of the commutator from its design roundness, accompanied by generation of spark discharges which eventually accelerate reduction in lifetime of the commutator. Accordingly, it is feasible that even during the high speed rotation of the commutator motor, the commutator can retain a rigid stability and a design roundness throughout the entire design lifetime and, for this reason, the commutators as assembled must be properly tested or evaluated.
Hitherto, a so-called run-out test method has been known as one of various methods of testing the commutator to evaluate the quality of the commutator as assembled. The details of the known run-out test method will now be discussed with particular reference to FIGS. 4 and 5 which illustrate a rotation testing apparatus and a roundness measuring apparatus, respectively, both of which are necessitated to accomplish the prior art run-out test method.
As shown in FIG. 4, a commutator 11 to be tested is mounted on and fastened by means of a nut 10 to a stud shaft 9 for rotation together therewith. The stud shaft 9 is in turn coupled to a main shaft 4 by means of a releasable chuck 5. The main shaft 4 is rotatably supported by a plurality of, for example, two bearings 3 and is drivingly coupled with an electric drive motor 1 by means of a generally endless drive belt trained between and around step-up pulleys 2. In this testing machine, the commutator 11 to be tested is driven about the main shaft 4 at a speed within the range of 10,000 to 50,000 rpm depending on testing conditions.
In order to simulate an actual operating condition of the commutator in which the commutator is subjected to thermal stress, heated air is supplied by a heater-equipped fan 6 into a simulating chamber 7 enclosing the commutator 11 on the stud shaft 9 so that the commutator 11 to be tested can receive the thermal stress of a magnitude comparable to that that would be imposed on the commutator during actual rotation thereof. A thermometer 8 persistently monitors the temperature to keep the temperature inside the simulating chamber 7 within the range of 200.degree. to 300.degree. C.
The commutator 11 to be tested is tested under this condition for a predetermined length of time with the use of the rotation testing machine shown in FIG. 4, and the commutator 11 so tested is removed from the rotation testing machine and is then loaded in the roundness measuring machine shown in FIG. 5 after having been cooled to room temperatures.
The commutator 11 removed from the rotation testing machine is mounted on a tester shaft 22 of the roundness measuring apparatus which is supported by and extends between generally V-shaped blocks 21 and is driven by an electric drive motor 23 by means of a capstan roller 24 at a low speed. During the testing, an electric micrometer 25 is positioned adjacent the commutator 11 with a measurement probe thereof held in sliding contact with the commutator segments so that during rotation of the commutator 11 distortion and/or run-out of the commutator 11 from the design roundness can be measured by the measurement probe of the electric micrometer 25. A detection signal outputted from the electric micrometer 25 which is indicative of departure from the design roundness by reason of, for example, eccentricity of the commutator and/or radial lift of one or more of the commutator segments is, after having been amplified by an amplifier 26, recorded and/or displayed by a recorder 27.
In the practice of the prior art run-out test method discussed above, the rotation testing and the roundness measurement are different operations to be done separately and, therefore, the commutator 11 once subjected to the rotation test must be removed and is subsequently allowed to stand still for measurement of the residual strain. Because of this, the behavior of the commutator during a high speed rotation thereof cannot be assessed. Also, since vibration induced in the main shaft 4 when the latter is driven by the step-up pulleys 2 at a higher speed than that of the drive motor 1 and, also, vibration brought about by the bearings 3 on the main shaft 4 are both transmitted to the commutator 11 being tested, the commutator 11 being rotated together with the main shaft 4 undergoes fluctuation. Under these circumstances, no proper initial measurement condition is available and, therefore, it is not only difficult to evaluate the physical strength, but also to accomplish measurement of dynamic distortion and/or run-out of the commutator driven at a high speed.
Because of the reason discussed above, there is no way to ascertain the behavior of the commutator being tested and improvement in design of the commutator to increase the reliability is therefore limited. With the prior art system in which the thermal stress is applied to the commutator being tested, the hot air supplied from the fan 6 tends to be stirred up by a windage loss brought about by the high speed rotation of the commutator 11, making it difficult to retain the temperature at a predetermined value. In addition, complicated and time-consuming testing procedures have been required.